Assigitoe



Patented Mar. 20, i928@ Ninsraras HERMAN A. AFFEL, vOF,M llPLElFOOD, NEW JERSEY, ASSIGNOR 3.18 ATEERCAN TELE- .FHONE AND TELEGRAPZ- COMPANY, A CORPORATION D?? NEVI 'ZOB-E.

BEPEATER SYSTEM.

Application led December 24, 1925.

' has a band filter connected therewith, which Y band filters are capable of transmitting a plurality of separated bands, the filters of one circuit being complementary to the filters of the other circuit, that is to say, the bands transmitted by a filter of oner circuit will be thus suppressed by the filter of the other circuit, and vice versa.

The invention has other objects which will be apparent from the following description when read in connection with the attached drawing, of which Figure 1 shows schematically a form of embodiment of the invention, land Figs. 2 and 2A are graphs serving to illustrate the principle upon which the invention rests.

In Fig. l, Ll and L2 represent sections of a signal transmission circuit intended for two-way transmission. It will, of course, be understood that suitable terminal apparatus will be connected with the lines L, and L2,

' such as telephone subsets, in order to effect .two-way transmission. A, and A2 represent amplifiers in the one-way circuits of the 22- type amplifier, A, serving to amplify the signal received from the line L, for transmission over L2, and A2 being arranged to actin the opposite direction. BF BF2, BF3 and BF, represent band filters. yThe transmission characteristics of the filters BF, and BF2 are shown in Fig. 2, and the characteristics of BF3 and BF2 are shown in Fig. 2A. These gures which represent the relation between frequency and loss, that is, attentuation of the filters, show that each lter transmits a plurality of bands of frequencies and likewise suppresses a plurality of bands lying between the transmitted Serial No. 77,606.

bands. Thus the filters BF, and BF2 may transmit four bands, one representing the range between j', and +12; the second lying between f2 and /15 the third lying between j",

fifi

and f6; and a fourth lying between f, and f2. Y

ln similar manner the filters BF, and BF, transmit four bands which cover frequencies suppressed by the filters BF, and BF2. Thus, for example, t-he filters BF, and BF4 transmit a band between 72 and 2N2, which range of frequencies lies between f2 and f3. In like manner, the other bands transmitted by the filters BF3 and BF, represent frequencies which are suppressed by the filters BF, and BF2.

if it be assumed that the frequencies represented by 7', to f2 represent the range of the frequencies over the lines L, and L2, those frequencies that come within the range of the bands transmitted by the filters BF, and BF2 will pass through the amplifier A, and will be amplified and impressed upon the line L2. Since these frequencies are not within the range of those transmitted by the 4filters BF3 and BF2 they will not pass through the one-way circuit in the amplifier A2, and there can not be singing around the four-wire circuit constituting the amplifier. However, the filter BF, will select the bands of frequencies from those being transmitted over the line L2, and when such frequencies are amplified by A2, they will be impressed upon the line L,. lt will be seen, therefore,A that by suitable frequency selection singing may be prevented.

If the lines L, and L2 are intended for two-way transmission of speech, distortion of the speech as a result of this method of frequency selection may be minimized by increasing the number of bands transmitted by each of the lters in each of the one-way circuits, so that each important part of the speech range will be found in each one-way circuit. However, there should be, of course, no overlapping of the bands of the filters of the one-way circuits because singing would result at the frequency or frequencies lying within the Zone of the over lap.

While this invention has been disclosed as Yembodied in a particular form, it is to be understood, of course, that such form is merely illustrative of the invention and that it is capable of embodiment in other and different forms without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a signaling system, the combination with a transmission circuit of telephone transmitters connected at diiiferent points thereon lfor the two-way transmission of speech thereover, a repeater circuit com-Y prising two parallel branches connected with said transmission circuit between points ot' connection of the said telephone transmitters, each comprising an amplifier and a band filter, each of the said band Iilters being so designed and proportioned as to transmit a plurality of bands of frequencies, all of which bands lie within the limits of the speech band of frequencies, the bands transmitted by one of said filters lying between the bands transmitted by the other of said filters.

2i In a signaling system, the combination with a transmission circuit of telephone transmitters connected at different points thereon for A the two-way transmission of speech thereover, a repeater circuit comprising two parallel branches connected with said transmission circuit between points of connection of the said telephone transmitters, each comprising a unilateral amplifier and a band filter, each adapted to pass a plurality of bands ot frequencies, all of which bands lie within the limits of the speech band oi" frequencies, the bands transmitted by one ofsaid filters lying between the bands transmitted by the other of said lilters.

3. In a signaling system, the combination with a transmission circuit of telephone transmitters connected at different points thereon for the two-way transmission of speech thereover, a repeater circuit comprising two parallel branches connected with said transmission circuit between points of connection of the said telephone transmitters, the said branches being designed for one-way transmission in relatively opposite directions, each branch comprising a unilateral device and a plurality or' filters adapted to pass a plurality ol bands of frequencies, the bands passed y the filters of one branch lying between the bands passed by the filters of the other branch, all of said bands lying within the limits ofthe speech band of frequencies. y Y

4. In a signaling system of the type set forth in claim l, themethod for preventing singing which consists in selecting a plurality of bands of frequencies throughout the range of the speech frequencies being transmitted in one direction, amplifying the selected bands and transmitting them in one direction, then selecting a plurality of bands of the speech frequencies being transmitted in the opposite direction, the latter selected bands lying within the frequency spectrum between the said first selected bands, amplifying the latter selected bands and transmitting the said bands as thus amplified in opposite direction to the first selected bands.

5.. In a signaling system of the type set forth in claim l, the method of preventing singing of the repeater, which consists in dividing the range of speech frequencies into a plurality of bands, selectingy one group of alternate ands of the said speech frequencies for amplilication and transmission in one direction, selecting the other group of alternate bands of said speech frequencies, amplifying and transmitting them in the opposite direction.

In testimony whereof, I have signed my name to this specification this 23rd day of December, 1925.

HERMAN A. AFFEL, 

